1. Technical Field of the Invention
The present invention relates to an optical fiber strain-measuring apparatus which measures the strain of an optical fiber by way of inputting light pulses into an optical fiber, detecting, and analyzing the generated natural Brillouin scattering of light.
2. Description of the Related Art
An optical fiber strain-measuring apparatus, generally, inputs light pulses into one end of a test optical fiber, removes the back scattered light which is generated within the test optical fiber from the same end as that where the above light pulses are inputted, heterodyne detects with a photo detector the multiplexed light which has multiplexed the extracted back scattered light with a continuous light (reference light) having a fixed wavelength, and from the relationship between the detected signals and the time elapsed since the inputting of the above light pulses, measures the strain position of the test optical fiber.
In recent years, an optical fiber strain-measuring apparatus to measure the strain and the like of a test optical fiber by means of inputting light pulses into a test optical fiber, detecting, and analyzing the natural Brillouin scattered light generated within the test optical fiber has been conceived. An apparatus which employs an Optical Fiber Ring Laser can be given as an example of an apparatus which measures the properties of an optical fiber by means of detecting the natural Brillouin scattered light.
This apparatus measures the strain of a test optical fiber by means of having an optical ring comprising an acousto-optic switch for pulsing the natural Brillouin scattered light outputted from the test optical fiber, inputting into the optical ring the light pulses having a prescribed wavelength, and heterodyne detects the outputted natural Brillouin scattered light which have been pulsed.
The acousto-optic switch is provided for obtaining only the natural Brillouin scattered light generated from a prescribed position within the test optical fiber.
However, conventional apparatuses have a disadvantage where the natural Brillouin scattered light obtained by the acousto-optic switch is limited to only the natural Brillouin scattered light generated at a prescribed position within the test optical fiber.
Additionally, there is a disadvantage, when heterodyne detecting, where the frequency band of the synthesized light which synthesizes the frequency of the natural Brillouin scattered light and the reference light is high, ranging approximately from 10 to 12 GHz, and makes detecting difficult.
Furthermore, since the cycle of the light pulse inputted into the optical ring is set to the amount of time needed for the light pulse to circle the entire length of the optical ring, there is a disadvantage that once the length of the optical ring is set, an extremely burdensome process ensues when the ring length of the optical ring is changed at a later time.